388 research outputs found
The ATLAS-SPT Radio Survey of Cluster Galaxies
Using a high-performance computing cluster to mosaic 4,787 pointings, we have
imaged the 100 sq. deg. South Pole Telescope (SPT) deep-field at 2.1 GHz using
the Australian Telescope Compact Array to an rms of 80 Jy and a resolution
of 8". Our goal is to generate an independent sample of radio-selected galaxy
clusters to study how the radio properties compare with cluster properties at
other wavelengths, over a wide range of redshifts in order to construct a
timeline of their evolution out to . A preliminary analysis of the
source catalogue suggests there is no spatial correlation between the clusters
identified in the SPT-SZ catalogue and our wide-angle tail galaxies.Comment: 9 pages, 4 figures. Submitted to Proceedings of Science for "The many
facets of extragalactic radio surveys: towards new scientific challenges",
Bologna, Italy 20-23 October 2015 (EXTRA-RADSUR2015
Advances on the morphological classification of radio galaxiesreview: A review
Modern radio telescopes will generate, on a daily basis, data sets on the scale of exabytes for systems like the Square Kilometre Array (SKA). Massive data sets are a source of unknown and rare astrophysical phenomena that lead to discoveries. Nonetheless, this is only plausible with the exploitation of machine learning to complement human-aided and traditional statistical techniques. Recently, there has been a surge in scientific publications focusing on the use of machine/deep learning in radio astronomy, addressing challenges such as source extraction, morphological classification, and anomaly detection. This study provides a comprehensive and concise overview of the use of machine learning techniques for the morphological classification of radio galaxies. It summarizes the recent literature on this topic, highlighting the main challenges, achievements, state-of-the-art methods, and the future research directions in the field. The application of machine learning in radio astronomy has led to a new paradigm shift and a revolution in the automation of complex data processes. However, the optimal exploitation of machine/deep learning in radio astronomy, calls for continued collaborative efforts in the creation of high-resolution annotated data sets. This is especially true in the case of modern telescopes like MeerKAT and the LOw-Frequency ARray (LOFAR). Additionally, it is important to consider the potential benefits of utilizing multi-channel data cubes and algorithms that can leverage massive datasets without relying solely on annotated datasets for radio galaxy classification.<br/
Radio imaging of core-dominated high redshift quasars
VLA imaging at kiloparsec-scale resolution of sixteen core-dominated
radio-loud QSOs is presented. Many objects appear to display variable radio
emission and their radio morphologies are significantly smaller than those of
steep-spectrum quasars, consistent with these objects being observed at sight
lines close to their (relativistic, 4-7) jet axes. The
usefulness of the radio source orientation indicator R_V, being defined as
ratio of radio core and rest frame optical V-band luminosity, is confirmed.Comment: 11 pages, 11 postscript figures, uses aa.cls 4.03 for LaTeX2e To
appear in Astronomy and Astrophysic
WATCAT: a tale of wide-angle tailed radio galaxies
We present a catalog of 47 wide-angle tailed radio galaxies (WATs), the
WATCAT; these galaxies were selected by combining observations from the
National Radio Astronomy Observatory/Very Large Array Sky Survey (NVSS), the
Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), and the Sloan
Digital Sky Survey (SDSS), and mainly built including a radio morphological
classification. We included in the catalog only radio sources showing two-sided
jets with two clear "warmspots" (i.e., jet knots as bright as 20% of the
nucleus) lying on the opposite side of the radio core, and having classical
extended emission resembling a plume beyond them. The catalog is limited to
redshifts z 0.15, and lists only sources with radio emission extended
beyond 30 kpc from the host galaxy. We found that host galaxies of WATCAT
sources are all luminous (-20.5 Mr -23.7), red early-type
galaxies with black hole masses in the range M M. The spectroscopic classification indicates that they
are all low-excitation galaxies (LEGs). Comparing WAT multifrequency properties
with those of FRI and FRII radio galaxies at the same redshifts, we conclude
that WATs show multifrequency properties remarkably similar to FRI radio
galaxies, having radio power of typical FRIIs
On the Populations of Radio Galaxies with Extended Morphology at z<0.3
Extended extragalactic radio sources have traditionally been classified into
FR I and II types, based on the ratio r of the separation S between the
brightest regions on either sides of the host galaxy and the total size T of
the radio source. Here we examine the distribution of various physical
properties as a function of r of 1040 luminous radio galaxies (RGs) at z<0.3
from the SDSS, NVSS, and FIRST. About 2/3 of the RGs are lobe-dominated (LD),
and 1/3 have prominent jets. If we follow the original definition of the FR
types (a division based solely on r), FR I and FR II RGs overlap in their host
galaxy properties. However, the rare, LD sources with r>0.8 AND OIII5007 line
luminosity >10^6 Lsun are markedly different on average from the rest of the
RGs, in the sense that they are hosted in lower mass galaxies, live in
relatively sparse environments, and have higher accretion rates onto the
central SMBH. Thus these objects and the rest of RGs form a well-defined
dichotomy. Motivated by the stark differences in the nuclear emission line
properties of the RG subsamples, we suggest that the accretion rate onto the
SMBH may play the primary role in creating the different morphologies. At
relatively high accretion rates, the accretion system may produce powerful jets
that create the "classical double" morphology (roughly corresponding to the LD
sources with r>0.8 and emission lines); at lower accretion rates the jets from
a radiatively inefficient accretion flow generate radio lobes without apparent
"hot spots" at the edge (corresponding to the majority of LD sources). At
slightly lower accretion rates AND in galaxies with dense galactic structure,
sources with prominent jets result. It is possible that while the high
accretion rate systems could affect sub-Mpc scale environments, the jets from
lower accretion rate systems may efficiently suppress activity within the host
galaxies.Comment: ApJ, accepted. 20 pages, 16 figures, 4 tables. Image quality of
Figures 1 & 2 degraded due to size limits. Table 4 is available and kept
up-to-date at http://member.ipmu.jp/yen-ting.lin/RG/index.html. Higher
resolution version available at
http://member.ipmu.jp/yen-ting.lin/Data/ytlin.pd
Investigating the large-scale environment of wide-angle tailed radio galaxies in the local Universe
We present a statistical analysis of the large-scale (up to 2 Mpc)
environment of an homogeneous and complete sample, both in radio and optical
selection, of wide-angle tailed radio galaxies (WATs) in the local Universe
(i.e., with redshifts 0.15). The analysis is carried out using the
parameters obtained from cosmological neighbors within 2 Mpc of the target
source. Results on WATs large-scale environments are then compared with that of
Fanaroff-Riley type I (FR Is) and type II (FR IIs) radio galaxies, listed in
two others homogeneous and complete catalogs, and selected with the same
criterion adopted for the WATs catalog. We obtain indication that at low
redshift WATs inhabit environments with a larger number of galaxies than that
of FR Is and FR IIs. In the explored redshift range, the physical size of the
galaxy group/cluster in which WATs reside appears to be almost constant with
respect to FR Is and FR IIs, being around 1 Mpc. From the distribution of the
concentration parameter, defined as the ratio between the number of
cosmological neighbors lying within 500 kpc and within 1 Mpc, we conclude that
WATs tend to inhabit the central region of the group/cluster in which they
reside, in agreement with the general paradigm that WATs are the cluster BCG.Comment: 8 pages, 5 figures, 1 table. Accepted for publication on A&
Origin of X-shaped radio-sources: further insights from the properties of their host galaxies
We analyze the properties of a sample of X-shaped radio-sources (XRSs). These
objects show, in addition to the main lobes, a pair of wings producing their
peculiar radio morphology. We obtain our sample by selecting from the initial
list of Cheung (2007, AJ, 133, 2097) the 53 galaxies with the better defined
wings and with available SDSS images. We identified the host galaxies and
measured their optical position angle, obtaining a positive result in 22 cases.
The orientation of the secondary radio structures shows a strong connection
with the optical axis, with all (but one) wing forming a angle larger than 40
degrees with the host major axis. The probability that this is compatible with
a uniform distribution is P = 0.9 10E-4. Spectra are available from the SDSS
for 28 XRSs. We modeled them to extract information on their emission lines and
stellar population properties. The sample is formed by approximately the same
number of high and low excitation galaxies (HEG and LEG); this classification
is essential for a proper comparison with non-winged radio-galaxies. XRSs
follow the same relations between radio and line luminosity defined by
radio-galaxies in the 3C sample. While in HEGs a young stellar population is
often present, this is not detected in the 13 LEGs, again in agreement with the
properties of non XRSs. The lack of young stars in LEGs support the idea that
they did not experiences a recent gas rich merger. The connection between the
optical axis and the wings orientation, as well as the stellar population and
emission lines properties, provide further support for an hydro-dynamic origin
of the radio-wings (for example associated with the expansion of the radio
cocoon in an asymmetric external medium) rather than with a change of
orientation of the jet axis.Comment: Accepted for publication in A&
Extragalactic Radio Continuum Surveys and the Transformation of Radio Astronomy
Next-generation radio surveys are about to transform radio astronomy by
discovering and studying tens of millions of previously unknown radio sources.
These surveys will provide new insights to understand the evolution of
galaxies, measuring the evolution of the cosmic star formation rate, and
rivalling traditional techniques in the measurement of fundamental cosmological
parameters. By observing a new volume of observational parameter space, they
are also likely to discover unexpected new phenomena. This review traces the
evolution of extragalactic radio continuum surveys from the earliest days of
radio astronomy to the present, and identifies the challenges that must be
overcome to achieve this transformational change.Comment: To be published in Nature Astronomy 18 Sept 201
- …